Production of chlorotrifluoroethylene polymer-in-monomer slurry



June 17, 1952 REARICK PRODUCTION OF CHLOROTRIFLUOROETHYLENE POLYMER-IN-MONOMER SLURRY Filed April 15, 1948 if., i Skwkwk /Illl m h wl Illn'l x c s MM l w.. r S M. .w E Y B 8.\m

Patented June 17, 1952 PRODUCTION- OF` CHLOROTRIFLUORO- ETHYLEN'E POLYMEYR-INFMONOMER:

SLURRY John S. Reariek, Summit, N. 3 assigner to 'lfhe M. W. KelloggCompany, Jersey City, `N. Jv., a*

corporation of Delaware Application Appuis, 194s,y serial No. 20,612, e ciaims; (ci. estL- 92.11

This invention relates to the manufacture of perhalocarbons. In one ofV its'aspects thisLinvention relates to the polymerization of perhaloolefins. In another aspect the invention relates particularly to the polymerization of triuoro# chloroethylene in aL continuous manner to produce a normally solid polymeric compound of high chemical and physical stability,

Under suitable reaction conditions 'trifluorochloroethylene canL be polymerized to produce a normally solid vpolymer or plastic of good physical and chemical propertiesand suitable for molding articles of manufacture and for various other uses. At the present time, polymerizationof triuorochloroethylene to produce solid polymers is effectedin a' batchmanner in a bomb type reaction vessel. Accordingly, the monomer ispintroduced into the bomb togetherwith a suitable promoter and the temperature of the bomb is maintained at about -16 or, 1'I C. for a period of about seven days. The monomer is converted to a porousplug of the solid polymer in the reac'# tion vessel with approximately 30 to 50 per cent yield of polymerbased onV the monomer charged. The unreacted monomer is occluded in the interstic'es'of the porous plug and is removed there from by heating the reaction Vvessel undersubatmospheric pressure so thatv the monomer is evaporated from the polymer plug. After' the monomer' has been thus evaporated, the-plug' is removed from the reaction vessel and broken vinto chips or granules,

The apparatus currently'emplcyed to effect the process described above is a cylindrical vessel or bomb approximately 6 inches in inside diameter, which is placed in a cooling bath. Because ofthe poor heat'transfer characteristics of the polymer it is necessary to maintain this cooling bath at a temperature materially below the optimum polymerization temperature to avoid overheating ofthe material in the'center of the reaction vessel. Experiments'in vessels of smaller diameter have indicated that the bath temperature caribe increased, and hence the average temperature of the material. without increasing the maximum temperatureofthe material at the center ofth'e0 vessel.' Because of the increaseof the average temperature, the rate of polymerization is greater, which factor results in .a shorter period of time to obtain an economical yield of product. There is also indication that the quality of!v the solid polymer produced is improved as a result ofthe greater uniformity of temperature characterized by smaller vessels. However, reduction inthe diameter of the vessel reduces the amount 2 of the material which can be produced for a given5 charge vsince the length ofthe vessel must be limited-"to` enable easy removal'A ofl the solid polymer from the vessel. It is, therefore, desirable to provide a method and apparatus for over? comingthe above difficulties involved. in the production of normally solid polymers of trifluoro chloroeth'ylene'.

The object of` this invention is to provide a continuous process` for',` the polymerization of polyfluorochloro-olens to produce normally solid polymers, l'

A moreispecic object of this invention is to provide a process 'forthej manufacturejo'f a nor? mally solid polymer of triuorochloroethylene;.`

Still another objectfofthis invention is to'provide a method, and apparatus for more adequate control ofl the temperature of reaction, in the polymerization' of trifluorochloroethylene than is at present practiced.

A further object of this inventionv is to provide a process, andVY apparatus for.' the' improvement in the quantity and reproducibility of normallysolid polymers of triuorochloroethylene;

it is stillV a further. object` of this invention to provide a process to increase the yieldjofno'rmally' solid` polymers of triuorochloroethylene.

-ifariojus other objects and 'advantages of the present invention will lznecornelapparentL to those' skilled in the art from'the 'accompanying de; scrption and disclosure.

[is herein employed, a perhaloc'arbon is derl'ed as a compound consisting substa'ntially'ofl carbon and halogen with any degree of` saturation'. A polyfluorochlormolefin is denned asia perhalocarbon, particularly a perhalo-olefin with' any degree or" unsaturation, consisting of iluorine, carbon and as' regards this invention not' more than one chlorine atom per atom of carbon.

In accordance with the continuous and improved process of thisinvention, a saturated'perfluorochlorocarbon is dechlorinated under suitable conditions ofdechlornationA` in the presence of a metallic dehalogenating/ agent to produce av perfluorochlorofolen asa monomer for'the subsequent polymerizationreaction. The declilorin` ation reaction is carried out in the presence of` a suitable solvent together .withla` minor proportion of ametal halide, which may be that formed during the dechlorin'ation reaction. and accord'- ing to the preferred'method` of operation of this invention the solvent is oney which is capable of dissolving the metal halide formed by the dehalogenation reaction and is higher'boilngfthan the'monom'er produced; An effluent comprising the desired monomer and including unreacted saturated perhalocarbon and solvent is passed to a fractional distillation system in which substantially pure monomer is recovered. Saturated perhalocarbon feed and solvent recovered from the monomer is returned to the dechlorination reaction zone. The monomer after further puriflcation is passed to a polymerization reaction zone in which it is subjected to suitable reaction conditions to convert the monomer to a normally solid polymer. The monomer is maintained in the liquid phase and under a sufficient degree of agitation in the polymerization reaction zone so that the normally solid polymer formed by the reaction, which is insoluble in the monomer, is caused to form a slurry therewith in the reaction zone. In effecting the reaction to produce the solid polymer a suitable catalytic material is used to promote the reaction. A portion of the liquid phase in the polymerization reaction zone is continuously removed therefrom as a slurry containing solid polymer particles and is passed to a filtration zone in which the solid particles are removed and the recovered unreacted monomer is recycled to the polymerization reaction zone. A portion of the monomer recovered from the slurry may be returned to the distillation system for repurication. The solid polymer is recovered as powder or granules and is treated to remove entrained monomer therefrom.

The slurry from the reaction zone is cooled and the rate of withdrawal and degree of cooling is controlled to maintain the reaction zone temperature at the desired value. The fluid nature of the slurry and the agitation in the reaction zone assures uniform temperatures for the polymerization reaction, while the recycle of cooled unreacted monomer removes the heat of polymerization.

For a better understanding of the present invention, reference will be made to the accompanying drawing which diagrammatically illustrates an arrangement of apparatus in elevation which may be used for the production of normally solid polymers of triuorochloroethylene. The principal pieces of apparatus for effecting the process depicted in the drawing comprises a dehalogenator 6, a polymerization reactor 44, separators 61 and 68 and various purification and separation equipment for puri- N fying and separating materials utilized and produced by the process.

According to the drawing and the process illustrated, trichlorotrifluoroethane of the 1,2,2, chloro-structure, which may be obtained commercially on the open market as Freon 113, is continuously passed through conduit 3 to dehalogenator 6. A metallic dechlorinating agent, such as zinc dust, is continuously or intermittently introduced through conduit 5 into reactor 6. Although zinc is preferred, various metal dechlorinating agents may be used, such as tin,

magnesium, and iron, without departing froml the scope of this invention. Fresh solvent of the general characteristics previously discussed is continuously or intermittently introduced into feed conduit 3 through conduit d, or alternatively directly into dehalogenator 6 by means not shown. In the discussion of the drawing, the solvent used in the dechlorination of trichlorotriuoroethane is methyl alcohol. IIhe amount of metal dechlorinating agent introduced into dehalogenator 6 is equivalent to at least the theoretical amount necessary for removal of twov halogen atoms from the halocarbon. Preferably,

an excess dechlorinating agent is used in effect-l ing the dechlorinating reaction and the excess may be as much as per cent or more. The amount of solvent may vary depending upon the reaction conditions, the quantity generally being less for superatmospheric than for atmospheric pressures, a suitable quantity for operation at atmospheric pressure being 65 per cent of the weight of the perhalocarbon charged.

, The mixture of perhalocarbon and solvent is vigorously agitated by conventional means, such as mechanical stirrer 8, to suspend the metal dechlorination agent in the liquid mixture in the lower portion of reactor 6. Required temperatures are maintained in the liquid phase of dehalogenator 6 by conventional means, such as heating or cooling coils 9 or a jacket through which a heat exchange medium is passed at the desired temperature. For a temperature below about 0 C., a light naphtha may conveniently be used. Water may be used for higher temperatures. Outlet conduit 1 is used for discharging the liquid contents of dehalogenator 6.

For the dechlorination of trichlorotrifluoroethane to trifluorochloroethylene, pressures between atmospheric and about 300 or 400 pounds per square inch gage are employed, preferably a pressure between about 20 and about 200 pounds per square inch gage, and a particularly suitable pressure is about pounds per square inch gage. In the preferred form of the invention, the pressure should be such at any given temperature to permit vaporization of the trifluorochloroethylene from the liquid phase in dehalogenator 6 without substantial vaporization of the other constituents of the reaction mixture. A suitable temperature for the dehalogenation is between about 0 C. and 200 C. It is preferred to use a temperature between about 40 and about 150 C., usually about 115 C. for operation at 180 pounds per square inch gage. At the higher temperatures the rate of reaction is increased, which in most instances is desirable. However, excessive temperatures cause undesirable side reactions.

In starting up the dehalogenation reaction a small proportion of a metal halide, such as zinc chloride, is introduced into dehalogenator 6 to promote or start the dehalogenation reaction. The metal halide may be introduced separately, or in admixture with the dehalogenating agent through conduit 5.

Suitable solvents for the dehalogenation step comprise methyl, ethyl, n-propyl, and n-butyl alcohols; dioxane. glycerol, butyl carbitol, and the Cellosolves. Other known solvents complying with the general requirements may be used, if desired, without departing from the scope of this invention. The preferred solvents are methyl alcohol and ethyl alcohol.

Since the temperature and pressure conditions which are maintained in dehalogenator 6 according to the preferred embodiment of this invention are such that the perhalo-olen formed therein as the desired product is vaporized, the olefin passes upward together with entrained and vaporized saturated perhalocarbons and solvent through a rectification column l i. The major proportion of the perhalocarbon and solvent are retained in the liquid phase in dehalogenator 6. The upper portion of the rectification column Il is maintained at a temperature substantially lower than the temperature of the liquid phase of dehalogenator 6, preferably at column II is maintained at the desired level by indirect heat exchange means I2 or by refluxing a portion of liqueed overhead product. In rectification column Il, methyl alcohol solvent and trichlorotrifluoroethaneare condensed and flow downward back ill-to dellalogenat'or 6, while the monomer is removed therefrom through conduit I3. Since rectification column II effects only a partial separation, the vaporo'us stream in conduit I3 will containminor amounts of url-'- removedtrichlorotrifluoroethane' and methyl alcohol'.

A typical composition of the trifluorochloroethylene-containing stream in conduit I3 is shown belowin Table I- for operation of dehalogenat'or 6 at a superatmosph'eric pressure of 87.5 pounds per square inch gage-andrectification column I' I at a top temperature. of about 24 C.

Table I Vol. per cent Monomer 98.0 Methyl alcohol 1.5 C2F3C13 0.1 Otherv materials l- 0.4

The monomer-containing stream vis passed through conduit I3 to a cooler I4, wherein it ls liquefied, and thence to a'fractional distillation column I6. As previously mentioned, a portion of the liquefied effluent in' conduit I3 may be returned by` means notjsll'own to the-upper portion of rectification column II as liquid reflux therefor to aid in maintenance of the required top temperature.

The` subsequent treatment of the effluent in conduit I3 is an important'feature of the process since the purification of the monomer trifluorochloroethylene bythe removal of the alcohol solvent andsaturated perhalocarbon is essential in orderto obtain satisfactory yields and repro ducible results in theV polymerization effected in reactor 441. To effect the purification of the monomer, liquid from conduit I3 is in one embodiment of this .invention introduced into fractional distillation column I6. This column is maintained at a temperature and pressure corresponding to that'required to pass monomer overhead and to recover the solvent and unreacted saturated perhalocarbon as a bottoms product. If superatmospheric pressures are em-V ployed during the dehalogenation in unit 6, the

pressure of the liquidin conduit I3 maybe decreased upon introduction into distillation column I6 toaid in thev fractional distillation and lower the temperatures required therein. Both' atmospheric and superatmospheric dis-tillations are feasible-and in some cases superatmospheric distillation may be preferred. A top temperature of about 20 C. is appropriate for atmospheric distillation in column I6: Indirect heat exchange element I1 isprovided in thev lower portion' of column I6' asa means for controlling the*L temperature of the bottoms product, the temperature of'whichisr-about 15 at atmospheric pressure. Element I1l may comprise-an-internal coil within column vI6 ora conventional external reboiler. Upon distillation, the monomer is removed from column I6 through conduit I8 together with a relatively minor proportion of. unremoved saturated halocarbon and also in some cases small amounts of methyl alcohol. The vaporous'eiiluent is:v passed through .conduit` It'r to a conventionalcoolerA :ir-,condenser lof-wherein the efiluent is condensed'. From cooler-i lg-fthe eilluen'tis; passed.

to anf accumulator 2-'I in which condensate is collected. A- por-tion` of the condensate is returned to column I6 throughconduit` 22l as liquid reflux therefor. Internalcooling'- means (not showt-D' may be positioned withini the upper porv tiori of column` I6 to' aid in refluxing'` ofthe dis tillation columnand may.' bei` used in addition to, or alternativelyv to, condensate. returnedthrough conduit 22. I

The' bottoms' product from distillation column I6 is removed therefrom through` outlet conduity 23 and-is returnedV by means of a pump (noti shown) 'throughconduits' 23 and 24`tol dehalo-v gen'atorf 6.' The bottoms'r product comprises the: majorAv proportionor' the solvent and saturatedper-halocax'fbon` in'- theA monomer-containing;- strearii' of conduit I3.

Analysisof a typical overhead productl ofco1-l umn- I-6- when it isfA operated atatop temperature ofabouit'! 209' C. and o; kettle temperature ori about-1ero.. atatmospheri'c pressure' indicates the,- pre'sencel of less th'an'- abo'ut one. per' centof` impurities, such as methyl alcohol and trifluoroi" trichloroethane.

Af-portion of the stream inconduit 23- maybe discarded'by` means noti shown in` orderl to' pre;-4

vent the-build-u'p of contaminant'ssinth'esysterm` sizioni-'asf.loy-productsY andY polymers formed dur-inethe': deh'aloge'naton; Liquid' can! also? be4 with'-l drawn. directly' fromv dehalogenator' e through outlet conduit. 1 for the above purpose.

In some` instances it mayl be'desi'rabl'ek toV use a soluble stabilizer orv inhibitorA to' prevent ciuda` tion and/or polymerization of Vthe monomer during distillation Aand storage.- Such soluble in'- hibitors: comprise a tertiary amine or'- terperie.

Condensatei from accumulator 2-I- isv passedI through conduit 251to a second fractional'-4 dis-V tillation column 26 in which solvent; and u reacted perhalocarbon are` removed from'- theV monomer. In column '26V the'. control' of tem;- peraturexand pressure'conditiorlslis more' selective' than in column' I 6 in -order to` malle'-v aclo'sercut" between' the monomerv andthe undesired ooi-ii'-` ponents, such as the solvent and satur'a't'ed'l per`v halocarbon. The temperature and pressure are selected such that the monomer is removed overhead through conduitv 28 and is passed through a cooler 29 to an accumulator 30. Condensate at a temperature of about-*28 C.- is returned to the top of column 26 through' conduit 32 as reflux. Solvent and saturated perhalocarbon are removed as a bottoms product through an outlet conduit 33. When operating at approximately atmospheric pressure the top temperature of column 26 is about 26 C. andthe kettle temperature of column 26 is about -2`0 C. Element 21 comprises a conventional heat exchange means, such as an internal coil or an external: reboiler, for' maintaining the desired temperatureat the bottom of column 26. A refrigerant, such as a light naphtha, iscirculated through coils- 21 at about -15 C. Solvent and unreacted monomer from reactor 4l" which have been sep-r arated from the solidv polymer product in separators 51 and 58 are introduced into the lower portion of column 26 through conduit BI. The solvent used in the polymerization for Adissolving the polymerization promoter and its recovery will be'discussed more fully hereinafter. Since the polymerization solvent is also higher boiling than-the monomer; it-is removed with the bottom product; through outle't conduit 33?.

For operating distillationv column 26 at a top ponent trichloroiiuoromethane, the solvent used in the polymerization step.

The liquid bottoms product from distillation column 26 continuously passes through conduit 33 to a third fractional distillation column 34 in which the solvent used in the polymerization step, such as CClsF, is separated from saturated perhalocarbon (CzFaCls) and solvent (methyl alcohol) used in the rehalogenatlon reaction. Temperature and pressure conditions of distillation column 34 are such that trichloroiiuorornethane is passed overhead while trichlorotriiiuoroethane and any remaining methyl alcohol are removed as a bottoms product. When using atmospheric pressure in distillation) column 34, the kettle temperature will be about 48 C. and the overhead temperature will be about 27 C. for separating trichlorouoromethane from trichlorotriiiuoroethane. For superatmospherlc pressures higher temperatures are used. The trichlorotrifluoroethane-containing bottoms product is removed from column 34 through outlet conduit 31 and is continuously returned by means of a pump (not shown) through conduit 24 to dehalogenator 6. Element 36 is a conventional heat exchange means, such as an internal coil or external reboiler, for controlling the kettle temperature of distillation column 34. The overhead product comprising trichlorouoromethane and less than about one per cent of the other components of the feed is removed from column 34 through conduit 46, a portion of which overhead may be condensed in a conventional cooler 41 and returned through conduit 49 to the upper portion of column 34 as reflux therefor. The treatment f the overhead product of column 34 and its return to reactor 44 will be discussed more fully subsequently.

The overhead product from the second dismonomer and traces of contaminants, such as methyl alcohol or other oxygen-containing compounds. This vaporous stream in conduit 28 is passed through a conventional cooler' 29 in which the vapors are cooled and condensedY and resulting condensate is passed from cooler 29 to an accumulator 30. Condensate which is collected in accumulator 30 is returned through conduit 32 to the upper portion of distillation column 2E as liquid reiiux for controlling the top temperature thereof. Alternatively or in addition to reiiuxing with condensate from conduit 32, internal cooling means (not shown) may be positioned within the upper portion of column 2S for causing internal reiiuxing.

If only that much of the vapors in conduit 28 are condensed as to provide reflux to column 2t,

the remaining vapors are removed from accumulator 30 through conduit 3| and are passed through treaters 39 and 4l, which are used alternately, to remove oxygen-containing compounds. While one treater is being used, the other treater is being filled with fresh treating agent or sorbent material or the sorbent material therein is being regenerated. Treaters 39 and4| contain suitable material for removingl traces of methyl alcohol and other oxygen-containing compounds present in the gaseous stream. Suitable treating agents or sorbents comprise phosphorous pentoxide, silica gel, activated carbon, and mixtures thereof; however, various other sorbents may be used which are known to those skilled in the art. Treaters 39 and 4i are used since a monomer of high purity is required in the polymerization of trifluorochloroethylene at a low temperature to produce a normally solid polymer of good physical and chemical properties. Preferably, treaters 39 and 40 contain alternate layers of phosphorous pentoxide and silica gel.

After passage of the monomer stream through treaters 39 or 4i, the stream is passed through conduit 42 to cooler 43 wherein the gaseous stream is cooled and condensed. From condenser or cooler 43, condensate at the desired temperature is passed to reactor 44. It is advantageous although not necessary to provide a cooled holding tank (not shown) to aid in the regulation of the flow of monomer to reactor 44.

To treat the monomer stream in the liquid condition Iin treaters 39 and 4I, cooler 29 is operated such that substantially the entire eluent stream in conduit 28 is condensed. Condensate from accumulator 30 is then passed through conduit 3S to treaters 39 and 4I, which are operated as described with respect to vapor phase operations. In this modification, cooler 43 may be omitted; however, cooler 43 may be used to further cool the condensate to the desired polymerization temperature after passage through treaters 39 and 4| without departing from the scope oi this invention.

Various methods and procedural steps for recovery and purification of the monomer may be practiced, although each method or procedure is not necessarily equivalent to the others. The steps for recovery and purification of the monomer depicted in the drawing is only one of several which may be followed to obtain a monomer of sufficient purity for producing a solid polymer of good physical and chemical characteristics. 'For example, the monomer-containing stream in conduit I3 may be treated with P205 prior to fractional distillation thereof and subsequent to distillation the monomer concentrate stream is treated with silica gel. The successive steps of treating the monomer stream with P205, distillation. and treating with silica gel renders a monomer of high purity. Another procedure consists of the steps of treating the monomercontaining stream of conduit I3 with P205 and then with silica gel. This latter procedure has been found satisfactory for purifying the monomer for subsequent polymerization to solid polymers without distillation. According to the procedure described with reference to the drawing, one of the distillation columns I6 or 26 may be eliminated without departing from the scope of this invention. The choice of the recovery and purification procedure used will depend upon the economic evaluation as well as such factors as the purity of the monomer desired, etc.

In reactor 44 liquid triuorochloroethylene is polymerized in the presence of an organic peroxide promoter to produce a solid polymeric material having good chemical and physical characteristics as a plastic. A particularly suitable promoter for the production of a solid product is bis-trichloroacetyl peroxide. The amount of trichloroacetyl peroxide used varies between about 0.01 and about0.15 per cent of the monoviluorometh'anefound capable of 'promoting 'the desired poly@ Amerization .reaction .to Yproduce .a normali' f solid polymerl of 'trlfluorochloroethylene.

Since the peroxide promoter is solid under normal conditions .and substantially insoluble in ther monomer, a .solvent is used to dissolve the promoter andthe resulting .solution of the promoter is injected finto reactor 4l .through conduit 5l. The use of the promoter as a solution facilitates handling and intimate mixing of the promoter with the monomer in the re` action zone. The preferred solvent is one which is nonreactive and has a boiling point higher than the boiling point of the monomer. The quantity of solvent containing the promoter employed is usually between about l vand about per cent of the monomer feed but larger or smaller amounts'may Vbe used without departing from the scope of this invention. The preferred solvent of the .presentV invention is trichloro maintained yat a sufficiently low temperature prior to introduction `into the reactor to minimize decomposition.

A solution of promoter is continuously or intermittently introduced into reactor 44 through conduit '51 after'being admixed with fresh or recycle solvent from conduit 55. Alternatively the solution of promoter may be injected into conduit 42 for adm-ixture with the monomer by means not shown. For the production of a normally solid polymer 'a temperature between -about -20 C. and about 150 C. is employed depending upon the promoter and other operating conditions used. Generally, however, somewhat higher temperatures can be used in the process of this invention than are possible for the batch-wise processes described previously. With a bis-trichloroacetyl peroxide promoter temperature between about -20 andV about 25 C. is preferred. rThe pressure should'be at least in lexcess of the vapor pressure of the monomer at the polymerization temperature employed.

The solid polymer of trfluorochloroethylene is formed -as fine particles suspended in the liquid monome'rbecause of 'its insolubility therein. The formation oi. the polymer as ne particles may be predicated to the fact that triiiuorochloroethylene polymerizes by nuclei growth. It is believed that the polymerization of the 4monomer to the solid polymer is accomplished in a rela 4tively short period of time and that the quantity of polymer produced .over a period of time is limited by the rate of formation of the polymer nuclei. As a result the bulk of monomer does not progressively polymerizein entirety. This theory is offered merelyas a means for better understanding the present invention and is not to be construed as limiting the invention or as the only explanation thereof.

The solution of promoter is` l0 be provided with cooling coils or acooling jacket (not shown) for aiding in the maintenance of the desired temperature therein. The form `of the reaction vessel is immaterial from the standpoint of this invention and the vessel may bein the form of elongated tubes or coils through which the kreaction mixture ows as a turbulent mixture. As shown in the drawing, however,the

reaction vessel is an enlarged zone in which is contained a substantial quantity of liquid monomer containing suspended solid polymer. VIn the enlarged vessel shown, the solid polymer is maintained in suspension by means of a .conventional mechanical stirrer 59. Stirrer 59 also `aids in maintaining uniform temperature throughout the liquid phase in the reaction vessel 44. The stirrer 59 ymay vbe 4omitted lif the liquid circulation within the vessel is suiciently great to maint-ain the polymer suspended in the-liquid monomer, such as the circulation vcaused by withdrawal and introduction of liquid.

In using a reaction coil `or tube of restricted cross section, the now through the reaction tube causes sufficient turbulence or agitation to maintain the solid particles vof monomer suspended -in the reaction mixture.

In accordance with this invention, -a slur-ry of monomer and solid polymer is removed at thedesired `rate from reactor 44 and passed .through conduit 6i by means of pump B2 to .cooler AE3. The slurry is cooled in ycooler 163 to -a temperature at least5 C. below the temperature of reactor 44 so that when the unreacted monomer .is recycled, the temperature ofthe reaction vessel is maintained substantially constant at the desired value bycontrolling lthe amount ofheat removed in cooler d3. From cooler 63 the cooled slurry is passed through either one of separating zones 61 and 68 through conduits 64 and E5, respectively. Separation units 61 `and t8 are used alternately. While one separating zone is on process flow the solid polymer is vbeing removed from the other separating zone. Any of the conventional filter means maybe used for separating the solid polymers Afrom the unreacted monomer. Such `lter means may comprise va conventionalplate and frame -lter press, a leaf lter, a rotary continuous lter, such as those disclosed in Elementsof Chemical Engineering, Badger and McCabe, McGraw VHill Book Company (1936), second edition. When a continuous filter is used, dual filters are unnecessary. On the other hand, separators 01 and 68 may comprise a settling zone in which the solid polymer is settled from the monomer Yand .accumulates in the bottom of the settling vessel from where it is removed through a Asuitable star .valve or the like. In the diagrammatic illustration shown in the drawing, the solid polymer isremoved from separators El and 68 through. outlet conduits @il and 1l, respectively.

Unreacted monomer is passed from separators 5l and E8 through conduits 1-2 and 13, respectively, and .is recycled -to reactor 44 through `conduits '14, l and 19. -A portion of the recycled monomer is returned -to distillation column 26 through conduit Si in order -to repuriiy the monomer. Usually the ratio of the amount of monomer recycled -to that diverted to distillation column l2b is about 1:1 to about -10zl 4by volume or higher, preferably a ratio of about 8:1 to about'zl.

Since acidic impurities, such as trichloroace-tic acid, phosgene and their derivatives, contaminate the monomer-containing stream, Vitis delet conduit 33.

11 sirable to remove these contaminants in order to prevent their build-up in the system and to prevent their adverse afect on the physical and chemical qualities of the solid polymer product. Such acidic impurities are removed from the recycle monomer stream by passing the stream through a treater 16 containing a suitable acid absorption medium, such as sodium or potassium hydroxide. A portion of the stream may by-pass treater 16 by means of conduit 11, if desired. If the monomer stream is treated in treater 16 with an aqueous alkali solution, driers (not shown) must be provided for removing traces of aqueous solution from the treated stream.

The monomer-containing stream in conduit 8l contains the solvent used for dissolving the promoter and in the particular embodiment of the invention described the solvent is trichlorofluoromethane. When the monomer-containing stream in conduit 8| is introduced into distillation column 26, the monomer is removed overhead as previously described and the solvent is removed with the bottoms product through out- This bottoms product from distillation column 26 is passed to a third distillation column 34 as previously discussed. In distillation column 34, trichloroiiuoromethane is continuously recovered as an overhead product and is passed through conduit 26 to a conventional cooler 41 in which at least a portion of the vaporous overhead product is condensed. Condensate is then passed to accumulator 48. From accumulator 48 condensate is recycled to the upper portion of column 34 through conduit 49 as liquid reflux therefor. When the entire overhead product is condensed in cooler 41 condensate is passed from accumulator 48 through con.- duit to treaters 53 and 54 to remove oxygencontaining compounds. When only the amount of overhead required for reflux in column 34 is condensed, the uncondensed overhead product is passed through conduit 52 through treaters 53 and 54. Treaters 53 and 54 are operated similarly and contain similar treating materials as were used in treaters 39 and 4I for removal of traces of methyl alcohol solvent which inhibits the polymerization reaction. As in the case of treaters 38 and 4l, treaters 53 and 44 are used alternately, while one is being regenerated or reu filled the other is on process flow.

Substantially pure trichloroiiuoromethane is returned to conduit 51 for admixture with promoter and for the subsequent introduction into reactor 44 through conduit 51.

Continuous removal of a slurry from reactor 44 and recovery of solid polymer from the slurry is the preferred method of operation in polymerizing triluorochloroethylene, but other methods may be used without departing from the scope of this invention. For example, a raking or elevating mechanism could be provided in the reaction vessel operating on a sloping bottom to remove the polymer particles as they settle to the bottom. Another modiiication is a rotating drum containing liquid monomer with a scraping means for removing the deposited polymer from the sides of the rotating drum.

The solid polymeric product recovered at 69 and 1l may be subjected to further treatment such as luorination, pyrolysis, drying, etc., without departing from the scope of this invention. Various modifications and alterations of equipment, such as elimination of one of the distillation steps, changes in the sequence of purification steps, and changes in the shape and/or size of reactor 44, may be practiced without departing from the scope of this invention. Certain pieces of apparatus and auxiliary equipment, such as liquid level controls, flow controls, temperature and pressure controls, valves, pumps, coolers or condensers and storage facilities have been omitted from the drawing as a matter of convenience and clarity.

Having described my invention, I claim:

1. A continuous process for polymerizing trifluorochloroethylene to produce a normally solid polymer of good physical and chemical characteristics which comprises the successive steps oi' introducing liquid triiluorochloroethylene and a solution of trichloroiiuoromethane and trichloroacetyl peroxide into a reaction zone, the amount of trichloroacetyl peroxide being between about 0.01 and about 0.15 per cent of the monomer charged, polymerizing trifluorochloroethylene at a temperature between about -20 and about 25 C. and a corresponding pressure to maintain the monomer in the liquid phase in said reaction zone to produce particles of solid polymer, agitating the reaction mixture to form a slurry of solid polymer and liquid monomer, continuously withdrawing from said reaction zone a slurry of said monomer and solid polymer, cooling the withdrawn slurry at least 5 C. below the prevailing temperature of said reaction zone, separating by ltration solid polymer as the product of the process and unreacted monomer from said slurry, treating at least a portion of the unreacted monomer thus recovered from the slurry with an alkali metal hydroxide to remove acidic impurities therefrom and recycling purified monomer to said reaction zone as feed thereto and as a. means for controlling the temperature thereof.

2. A continuous process for polymerizing triuorochloroethylene to produce a normally solid polymer which comprises the successive steps of introducing triiluorochloroethylene and a solution of trichlorouoromethane and trichloroacetyl peroxide into a reaction zone, polymerizing triuorochloroethylene at a temperature between about -20 and about 25 C. and at a pressure to maintain the monomer in the liquid phase in said reaction zone to produce particles of solid polymer, forming a slurry of solid polymer with liquid monomer in said reaction zone, continuously withdrawing from said reaction zone a slurry of said monomer and solid polymer. cooling the withdrawn slurry below the prevailing temperature of said reaction zone, separating by filtration solid polymer as the product of the process and unreacted monomer from said slurry, treating at least a portion of the unreacted monomer thus recovered from the slurry with an alkali to remove acidic impurities therefrom, rand recycling puried monomer to said reaction zone as feed as a means for controlling the temperature thereof.

3. A continuous process for polymerizing trifluorochloroethylene to produce a normally solid polymer of good physical and chemical characteristics which comprises the successive steps of introducing liquid triuorochloroethylene and a halogenated acyl peroxide which is effective under the polymerization conditions as a promoter into a reaction zone, polymerizing trifiuorochloroethylene at a temperature between about -20 and about 25 C. and a corresponding pressure to maintain the monomer in the liquid phase in said reaction zone to produce particles of solid polymer, agitating the reaction mixture to form a slurry of solid polymer and liquid monomer, continuously withdrawing from said reaction zone a slurry of said monomer and solid polymer, cooling the withdrawn slurry below the prevailing temperature of said reaction zone, separating from said slurry solid polymer as the product of the process and unreacted monomer, and recycling unreacted monomer to said reaction zone as feed thereto and as a means for controlling the temperature thereof.

4. A continuous process for polymerizing trifluorochloroethylene to produce a normally solid polymer which comprises the steps of introducing trifluorochloroethylene into a reaction zone, polymerizing trifluorochloroethylene at a temperature between about C. and about 25 C. in the presence of a halogenated acyl peroxide which is effective in the aforesaid temperature range as a promoter for the polymerization at a pressure to maintain the monomer in the liquid phase in said reaction zone to produce particles of solid polymer, agitating the reaction mixture to form a slurry of solid polymer with the liquid monomer, continuously withdrawing from said reaction zone a slurry of said monomer and solid polymer, cooling the withdrawn slurry below the prevailing temperature of said reaction zone, separating from said slurry solid polymer as the product of the process and unreacted monomer, and recycling cooled unreacted monomer to said reaction zone as feed thereto and as a means for controlling the temperature thereof.

5. A continuous process for polymerizing trifluorochloroethylene to produce a normally solid polymer of good physical and chemical characteristics which comprises the steps of introducing triuorochloroethylene into a reaction zone, polymerizing trifluorochloroethylene at a temperature between about -20 and about 25 C. in the presence of a halogenated acyl peroxide which is effective in the aforesaid temperature range as a promoter for the polymerization and at a corresponding pressure sufficient to maintain monomer in the liquid phase in said reaction zone to produce particles of solid polymer, withdrawing from said reaction zone a slurry comprising monomer and solid polymer, separating solid polymer as a product of the process and unreacted monomer from said slurry, and recycling said monomer to said reaction zone.

6. The improved process for polymerizing triuorochloroethylene which comprises introducing triuorochloroethylene into a reaction zone. in said reaction zone polymerizing trifluorochloroethylene in the presence of trichloroacetyl peroxide as a promoter at a temperature between about -20 and about 25 C. and at a corresponding pressure sufficient to maintain monomer in the liquid phase to produce particles of solid polymer in suspension in liquid monomer at the temperature of polymerization, and separating and recovering particles of solid polymer from the suspension as a product of the process.

7. The improved process for polymerizing trii'iuorochloroethylene which comprises introducing trifluorochloroethylene into a reaction zone, in said reaction zone polymerizing trifluoroohloroethylene at a temperature between about -20 and about 25 C. in the presence of a halogenated acyl peroxide which is effective in the aforesaid temperature range as a promoter for the polymerization and at a corresponding pressure sufficient to maintain monomer in the liquid phase to produce particles of solid polymer in suspension in liquid monomer at the temperature of polymerization, and separating and recovering particles of solid polymer from the suspension as a product of the process.

8. The process of claim 7 in which said organic peroxide promoter is chlcroacetyl peroxide.

9. The process of claim '7 in which said organic peroxide promoter is dichlorouoroacetyl peroxide.

JOI-IN S. REARICK.

REFERENCES CKTED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 2,345,659 Downes Apr. 4, 1944 2,396,791 Krase Mar. 19, 1946 2,531,134 Kropa Nov. 21, D FOREIGN PATENTS Number Country Date 796,026 France Mar. 27, 1936 OTHER REFERENCES Belmore et al., Ind. Eng. Chem., 39, 338-342 (March 1947). 

7. THE IMPROVED PROCESS FOR POLYMERIZING TRIFLUOROCHLOROETHYLENE WHICH COMPRISES INTRODUCING TRIFLUOROCHLOROETHYLENE INTO A REACTION ZONE, IN SAID REACTION ZONE POLYMERIZING TRIFLUOROCHLOROETHYLENE AT A TEMPERATURE BETWEEN ABOUT -20 AND ABOUT 25* C. IN THE PRESENCE OF A HALOGENATED ACYL PEROXIDE WHICH IS EFFECTIVE IN THE AFORESAID TERMPERATURE RANGE AS A PROMOTER FOR FTHE POLYMERIZATION AND AT A CORRESPONDING PRESSURE SUFFICIENT TO MAINTAIN MONOMER IN THE LIQUID PHASE TO PRODUCE PARTICLES OF SOLID POLYMER IN SUSPENSION IN LIQUID MONOMER AT THE TERPERATURE OF POLYMERIZATION, AND SEPARATING AND RECOVERING PARTICLES OF SOLID POLYMER FROM THE SUSPENSION AS A PRODUCT OF THE PROCESS. 